"My government's position is clear: US criminal law and treaty obligations prohibit torture. Torture is wrong," he said.

Mr Lowenkron said abuses carried out by US soldiers at Iraq's Abu Ghraib jail had been "inexcusable, they were indefensible".

But he noted that more than 250 people had been held accountable.

State Department legal adviser John Bellinger said the US welcomed the dialogue and would try to answer the committee's questions.

But he said incidents of abuse were "not systemic" and urged the panel "not to believe every allegation that you've heard".

"Allegations about US military or intelligence activities have become so hyperbolic as to be absurd," he said.

US Deputy Assistant Secretary of Defense Charles Stimson said 120 detainees had died in Iraq and Afghanistan, 29 of whom might have been abused.

He said suspected cases were investigated and "appropriate action taken".

The BBC's defence and security correspondent Rob Watson says the size of the delegation - nearly 30-strong - indicates the determination of the Bush administration to fight back against the numerous allegations over its treatment of terrorism suspects.

But he says it also seems to be an acknowledgement of the damage done to America's standing in the world.

Names and numbers

The committee has 59 questions for the US, 53 of which relate to the war on terror.

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The vast majority who are being held could hold information crucial to the war

Officials will be asked to provide a list of all secret detention centres, nationalities and numbers of those being held and the reasons for their detention.

The committee will also ask for details of detainees taken abroad to third countries, in a process known as extraordinary rendition.

It wants to know what measures the US has taken in the wake of the Abu Ghraib scandal to ensure that such abuse does not happen again.

They may also want to know if there has been an independent inquiry into the possibility that high-ranking government officials authorised torture.

Human rights campaigners say the hearings have huge significance.

"What makes this so remarkable is that this is the first time the United States is accountable for its record on torture with regard to some of the practices implemented after 9/11," said Jennifer Daskal of Human Rights Watch.

Amnesty International, which submitted a report to the panel, said US public statements contradicted its practices.

"The US government is not only failing to take steps to eradicate torture, it is actually creating a climate in which torture and other ill-treatment can flourish, including by trying to narrow the definition of torture," said group official Curt Goering.

Ten legal experts will cross-examine the US team until Monday and the committee will publish its recommendations at a later date.

The US is obliged by the UN convention to implement the recommendations, although there is no enforcement mechanism.

But a damning report from the committee would clearly add to the administration's difficulties in defending its approach to terrorism suspects, our correspondent says.